The present invention relates to internal combustion engines, particularly single cylinder internal combustion engines such as those used to power lawnmowers, sump pumps, portable generators and other devices. More specifically, the present invention relates to a twin cam design and related oil circuit for implementation in such engines.
Single cylinder internal combustion engines typically employ an intake valve and an exhaust valve for allowing fuel and air to enter the engine cylinder and allowing exhaust to exit the cylinder, respectively. These valves often are actuated by way of valve trains that impart linear movement to the valves in response to rotational movement of cams. In many such engines, the intake and exhaust valves are actuated in one direction (to close) by respective springs and actuated in the opposite direction (to open) by respective rocker arms. The rocker arms in turn are actuated by respective push rods that ride along respective cams that are supported by and rotate about a camshaft, which in turn is driven by a crankshaft of the engine. A fan also driven by the crankshaft blows air across the cylinder to cool the cylinder.
In such engines, it is important that oil or other lubrication be provided to at least the main bearings for the crankshaft and the camshaft, and that such oil be filtered. Consequently, most single cylinder engines also have carefully-designed lubrication systems to provide the necessary lubrication. The lubrication systems typically include an oil reservoir, a pump, and an oil circuit consisting of a series of passages by which oil is directed from the pump to the oil filter and to the components requiring lubrication. The oil passages are commonly manufactured by drilling or casting tubes into the crankcase and cover/oil pan of the engine.
Single cylinder engines of this design have several limitations. To begin with, the push rods that are positioned on such engines in between the camshaft and the rocker arms are positioned close together on a single side of the cylinder. Likewise, the pair of rocker arms at the cylinder head are positioned close together along a single side of the cylinder head, as are the pair of valves. Consequently, the valve bridge area of the cylinder head in between the valves, which is the hottest area of the cylinder head, is narrow and partially shielded from air being blown across the cylinder head by the fan. As a result, the valve bridge area may not be cooled as well as might be desirable, which can eventually cause weakening or breakage of the cylinder head, or to distortion/movement of the valve seats adjacent to this valve bridge area.
Additionally, the oil circuits in such single cylinder engines are often complicated in design and expensive to manufacture. In particular, the drilling or casting that is required in order to provide the required oil passages within the crankcase walls and cover/oil pan can be expensive and difficult to manufacture. The casting of tubular passages in particular is expensive insofar as it requires the use of cores.
Further, given their complexity and large number of moving parts, the valve trains (including the camshaft and crankshaft) of such engines also can be difficult and costly to design and manufacture. For example, the two cams on a camshaft of such an engine typically must be oriented differently so that their respective main cam lobes are 100 or more degrees apart. Consequently, the manufacture of a camshaft with two such differently-oriented cams can be difficult and expensive, particularly when it is desired to integrally form the camshaft and cams as a single part. The costs of manufacturing of such valve train components can be further exacerbated if it is desired to manufacture such components from materials that are more durable or that provide quieter operation, since it is typically more difficult to mold or machine complex parts from such materials.
It would therefore be advantageous if a new single cylinder engine was designed that avoided or suffered less from the above problems. In particular, it would be advantageous if a single cylinder engine with robust, quietly-operating components could be designed that was more easily and cost-effectively manufactured than conventional engines, particularly in terms of the costs associated with the components of its valve train and lubrication system. Further, it would be advantageous if a single cylinder engine could be designed in which there was more effective cooling of the valve bridge area than in conventional engines.
The present inventors have discovered a new, twin-cam single cylinder engine design having two camshafts that are each driven by the crankshaft. Because two camshafts are employed, one of which drives a valve train for an intake valve and one of which drives a valve train for an exhaust valve, the valves are respectively positioned on opposite sides of the cylinder so that the valve bridge area is exposed to allow for more effective cooling of that area. Each of the twin camshafts includes a respective internal passage extending the length of the respective camshaft. One of the camshafts is supported by an oil pump. Rotation of that camshaft drives the pump, causing oil to be pumped toward a lower bearing of the crankshaft and also up through the internal passage in that camshaft.
The oil is then directed through molded passages within a top of the crankcase, to an oil filter, to an upper bearing of the crankshaft, and to the other camshaft. It further flows through the internal passage of that other camshaft to the lower bearing of that camshaft. The passages within the top of the crankcase are formed by molding grooves in the top and covering those grooves with an additional plate. Because twin camshafts are employed, each of which has only a single cam lobe, the camshafts can more easily be manufactured from robust, quietly-operating materials. Additionally, by employing the passages within the top of the crankcase and within the camshafts, manufacture of the crankshaft oil circuit is simpler and more cost-effective than in conventional engine designs.
In particular, the present invention relates to an internal combustion engine including a crankcase having a floor, a pump supported by the floor of the crankcase, and a first camshaft. The pump includes an inlet and a first outlet. The first camshaft has a first cam, first and second camshaft ends, and a first internal channel extending within the first camshaft between the first and second camshaft ends. The first camshaft end is supported by one of the pump and the floor. Rotation of the first camshaft causes the pump to draw in lubricant via the inlet and to pump out at least a first portion of the lubricant via the first outlet. The first outlet is positioned in proximity to the first internal channel at the first camshaft end, so that at least some of the first portion of the lubricant pumped out via the first outlet is pumped into the first internal channel.
The present invention further relates to an internal combustion engine including means for converting rotational motion imparted by a crankshaft into linear motion used to actuate a valve. The internal combustion engine additionally includes means for pumping lubricant, and means for communicating the lubricant through at least a portion of the means for converting. The means for pumping is actuated by the means for converting, and the means for pumping pumps the lubricant into the means for communicating so that the lubricant is provided to a component requiring the lubricant.
The present invention additionally relates to a method of distributing lubricant within an internal combustion engine. The method includes providing a crankshaft, a first camshaft having an internal channel extending between first and second ends of the first camshaft, a pump having an inlet and an outlet, and a first bearing for the first end of the first camshaft, where the outlet is proximate the first bearing and the internal channel at the first end of the first camshaft. The method further includes rotating the crankshaft, imparting rotational motion from the crankshaft to the first camshaft, and imparting additional rotational motion from the first camshaft to at least a portion of the pump. The method additionally includes pumping the lubricant from the inlet of the pump to the outlet of the pump as a result of the additional rotational motion, so that a first portion of the lubricant is provided to the first bearing and a second portion of the lubricant is pumped into the internal channel at the first end of the first camshaft so that the lubricant is communicated through the internal channel to the second end of the first camshaft.